Precise control of fluid flow at the micrometer-scale (microscale) and nanometer-scale (nanoscale) level has enormous technological applications. For example, many recently developed microfluidic applications of chemical and biochemical analysis using lab-on-a-chip technology require the controlled flow of fluids at the microscale level. The burgeoning disciplines of genomics and proteomics demand a fast, efficient, and high throughput biomolecular separation technology that can be carried out on a chip format.
Microscale separation technologies typically employ microfluidic channels together with high voltages applied to built-in electrodes for movement of fluids on a substrate surface, such as those taught in U.S. Pat. No. 7,033,476, to Lee et al. on Apr. 25, 2006 and, U.S. Pat. No. 7,211,181 to Thundat et al., on May 1, 2007, and WO2005100541 A2 to the Univ. of California as published on Oct. 27, 2005. The use of a high voltage on a fluidic chip is one of the main disadvantages in the present-day practice of the microfluidic analysis using lab-on-a chip technology. Like microheaters, microfluidic channels cannot be reconfigured once they have been fabricated.
It is also known to manipulate a liquid on a surface by altering the temperature of the liquid. A temperature change effected at the interface between the surface and the liquid will move the liquid by the change in surface tension. For pure liquids, the surface tension decreases as a function of increasing temperature. Since surface tension has the dimensions of N/m (a force), any gradient in surface tension is a pressure. The pressure difference can cause substantial fluid transport due to the Marangoni effect.
These kinds of temperature changes are usually affected by microheaters constructed on a substrate surface. Microheaters make the device expensive to fabricate, and in addition, once they have been fabricated, the heaters cannot be reconfigured.